Variable tuning system



Jan. 4, 1944. w. F. SANDS ET AL VARIABLE TUNING SYSTEM Filed July 1, 1941 Bnnentots Patented Jan. 4, 1944 7 VARIABLE TUNING SYSTEM William F. Sands and George M. Daly, West Collinmood; N.

1., minors to Radio Corporation oi America, a corporation of Delaware Application July 1, 1941, Serial No. 400,824,

Claims.

This invention relates to variable tuning systems for radio signal receiving apparatus and the like. More particularly, the invention relates to a variable tuning system for the signal input and oscillator circuits of a superheterodyne receiver, and has for its primary object, to provide a compact and simplified tuning system for such circuits in a single unit, whereby the system is adapted for use in miniature portable receivers of the personal or pocket type.

It is a further object of this invention, to provide a unitary, relatively wide range, variable a tuning system for the signal input and oscillator circuits of a superheterodyne receiver which includes variable permeability tuning of an oscillator circuit and variable capacity tuning of a signal input or antenna circuit with unitary tuning means adapted to occupy minimum space in a receiver.

It is a still further object of this invention, to provide a combined variable permeability tuning inductance and a variable capacitor having fixed and movable elements arranged in eeaxial relation to provide a compact unitary tuning system for high frequency signal circuits.

As is well known, in the tuning of a superheterodyne receiver, a loop antenna is, often used both as a tuning inductance and as a signal collecting means for the input circuit and is therefore effectively tunable through a predetermined frequency range such as the broadcast band, by variable capacitor means. The oscillator, however, is then tunable preferably by means'oi a movable tuning core or variable permeability inductance. The latter inductance may be shielded electro-magnetically and may also be provided with an outer magnetic sleeve for preventing eddy current losses in the first named shield means.

It is, therefore, a further object of this invention, to provide a modified shield and core arrangement for a variable permeability tuning inductance which permits variable capacity tuning of an additional circuit in unison with variations in the tuning of a circuit connected with the variable permeability tuning inductance.

It is also a further object of this invention, to provide a unitary tuning system providing conjoint tuning control of a variable capacitor and a variable inductance having the movable and fixed elements thereof coaxially arranged and being coextensively movable, whereby simultaneous variation of tuning capacity and inductance in unison or predetermined tracking relation is eifected.

It is also an object of this invention, to provide a tuning system of the type referredto which may readily be constructed at low cost and which is particularly adapted for use in miniature receivers of the pocket or personal t p In its present preferred form as applied to a superheterodyne type of receiver fortuning the loop or signal input and oscillator circuits thereof, the invention comprises a single unit coaxial type tuner including a permeability tuned inductance coaxial and coextensive with a coaxial type variable capacitor, thevariable permeability tuning element being placed coaxially within the variable capacitor elements which serve as a shield. In addition, a magnetic sleeve may be used between the oscillator inductance winding and the inner cylinder or element of the capacitor to improve the Q of the coil and to extend the tuning range. A coating of fairly high dielectric constant is placed on one of the engaging surfaces of the variable capacitor portion of the tuning unit to provide a desired maximum capacity and to insulate the movable and fixed elements.

The invention will, however, be further understood from the following description, when considered in connection with the accompanying drawing, and its scope is pointed out in the appended claims.

In the drawing,

Figure 1 is a view on a greatly enlarged scale and partly in cross-section showing a tuning system embodying the invention, 7

Figure 2 is a schematic circuit diagram showing the circuit connections for the system of Fig. 1 in a superheterodyne receiving system,

Figure 3 is a graph showing curves illustrating certain tuning characteristics of the system of Figs. 1 and 2, and

Figures 4 and 5 are fragmentary views partly in section and on the same scale as Fig, 1 showing modifications thereof.

Referring to Figs. 1, 2 and 4, an elongated- The oscillator cathode, grid and anode electrodes 8, 9 and I0, respectively, are contained in a suitable combined detector-oscillator tube II. The signal input grid of the device II is indicated at I! and is connected to a signal input circuit l3 comprising a loop antenna or inductance ii and a shunt variable tuning capacitor II comprising a fixed grounded electrode l6 and a movable electrode l1.

Intermediate frequency signals are derived from the device ll through the output anode circuit l8 and a suitable tuned intermediate frequency coupling transformer i9. As the circuit is shown only for the purpose of illustrating a present preferred use for the variable inductance and capacity elements of the tuning system, further description of the mixer tube and other circuits of the receiver is believed to be unnecessary.

The inductance winding is carried preferably by an insulating coil form 25 which is supported in a rubber bushing 26 or other suitable mounting means, in one arm 21 of a supporting frame 28.

The fixed element I6 of the variable capacitor means is a tubular shell having a partially closed end 30 supported by and mounted in a rubber bushing 3| or other suitable flexible or non-rigid supporting element carried by the coil form 25. The movable portion or element I "I of the variable capacitor means is a tubular member supported at one end on a shouldered insulating base 32 secured to a longitudinally movable frame or carrier member 33 which slides on two guide rods 34 extending longitudinally on opposite sides of the tuning unit between the arm 21 and an opposite arm 35 of the fixed frame 28.

The carrier member or frame 33 is moved by any suitable means such as a tuning control knob indicated at 36 through the medium of a cord 31 wrapped about the spindle 38 of the knob and connected with the frame as indicated at 39 and 40 to cause the frame 33 to move along the rods 34 when the shaft 38 is turned. In this case two idler wheels or pulleys 4| serve to guide the cord to produce longitudinal movement of the frame with respect to the axis of the tuning unit. Any other suitable arrangement, however, may be utilized for guiding. supporting and moving the capacitor element H.

The core 6 of the tuning inductance is con- Jointly movable with the capacitor element l'l' through a connection provided by a flexible wire or other suitable flexible element 42 embedded in the core 6 and connected with a screw threaded spindle 43 mounted in the insulating support 32. A clearance opening 44 is provided about the element 42 in the movable frame 33 whereby the core 6 is insulated from ground or'chassis.

Electrical connections are made to the outer cylinder or electrode ll through any suitable means such as a flexible conductor 45 connected with a terminal 46. In the case of the inner electrode l6, connection is made thereto by a conducting sleeve 41 referably of copper, contacting the inner wall of the cylinder I6 and connected through a conductor 48 with a terminal 49. In order to insulate the two elements of the variable capacitor, a layer of insulating material indicated at 50 is placed on the outer cylinder although it may be placed on the inner face of the outer cylinder as well. This coating should be of relatively high dielectric constant to provide a suflicient capacity for tuning a circuit through a desired frequency rangewhen the outer and inner cylinders are fully concentric.

In the case of the arrangement of Fig. 4 the connection 48 is made directly with the inner cylinder Hi. It will be noted that in this fig re, as distinguished from the construction of the device of Fig. 1 wherein an outer magnetic sleeve member 52 is provided to confine the flux and to prevent any possibility of eddy current loss in the shielding or capacitor elements, the construction is of lower cost and of lighter weight for use in miniature portable receivers andthe like.

The use of the sleeve 52 surrounding the winding throughout its length improves the Q of the coil and extends the tuning or inductance variation range, provided by movement of the core from a position without to a position fully within the winding.

1 Th tracking relation between the tuning of a circuit containing the inductance winding 5 and a circuit containing the elements l6 and I1 as a variable capacitor, for example as shown in Fig. 2, is indicated in Fig. 3 by the curves 55 and 56, respectively. It will be noted that in moving thecore and the capacitor element l'l through a range of movement of substantially one inch, the tuning of the system is'caused to pass through a frequency range of substantially 550 to 1600 kc. which covers the present broadcast range, and that the tuning of the two circuits is in substantial tracking alignment throughout.

The initial tracking relation between the two circuits is provided by adjustment of the core 6 by means of the threaded spindle 42. This may be turned to cause the core to be moved with respect to the capacitor element 1 I thereby to vary the inductance of the winding 5 with respect to the tuning of the loop or other circuit associated with the capacitor means.

A further aid in obtaining the tracking relation between the tuning of the two elements or circuits, as indicated by the curves 55 and 58 of Fig. 3, is obtained by making the oscillator or inductance winding 5 of variable pitch as indicated. In one embodiment of the invention, the initial -turns at the entering end of the core includes a short section as indicated, having a winding pitch of the order of turns per inch, followed by a longer intermediate section havin a winding pitch of the order of 116 turns per inch, and a final low frequency end section having a winding pitch of the order of 92 turns per inch.

A has been pointed out hereinbefore, the construction shown in Figs. 1 and 4 is on a greatly enlarged scale. For example, the cell length may be substantially and the coil form 25 may have an outside diameter of .22" in actual practice. The outside diameter of the outer cylinder may be substantially and the overall length of the tuning system may be approximately 2%".

I Thu it is readily adapted for usein miniature receivers and the like where space and weight requirements as well as simplified low cost construction is essential.

Referring now to Fig. 5 wherein the same reference numerals as in Figs. 1 and 4 are used for like parts, in case the outer cylindrical magnetic sleeve 52 is provided, insulating supporting sleeves indicated at 60 are provided as in the embodiment shown' in Fig. 1 so that the core or sleeve is slightly out of contact with the winding. In this case, however, the inner electrode of the variable capacitor is provided by a coating of conducting material 6| on the magnetic sleeve 52 to which the connection 48 is made as indicated, and an insulating dielectric coating indicated at 62 is provided to separate the outer sleeve l1 therefrom as it moves in response to tuning control. This appreciably simplifies the system and reduces the weight although the cost of construction is slightly higher because of the use of the outer core or sleeve 52 and the processes involved in coating the latter. 7

Terminal connections for the windings are indicated at 63 and 64 in Fig. 1 although the actual connections with the winding are omitted for the purpose of simplifying the drawing.

While the invention has been described in its preferred application to the tuning of a superheterodyne receiving system, it is not limited thereto, but may be utilized in connection with any circuits which may be conjointly tunable by means of a variable inductance and a variable capacitor having a predetermined tracking relation throughout the tuning range.

We claim as our invention: 1

1. A variable permeabilitytuning system comprising in combination, a variable permeability tuning inductance, a variable capacitor having fixed and movable elements arranged in coaxial relation with each other and with said inductance to provide a compact unitary tuning device, and means providing a fixedmagnetio sleeve element between said variable capacitor elements and said tuning inductance.

2. In a variable permeability tuning system, a variable permeability tuning inductance comprising an elongated winding, an elongated movable rod-like magnetic core for said winding, a magnetic shield surrounding said winding in spaced coaxial relation thereto, said systemhaving an inner fixed portion and an outer portion movable in unison with said core to provide a variable capacity with the fixed portion, and means providing an adjustable connection between said core and said movable portion.

3. In a variable permeability tuning system, a tunable circuit including a variable permeability tuning inductance comprising an elongated winding, an elongated movable rod-like magnetic core for said winding, a shield comprising a sleeve of magnetic material surrounding said winding in fixed relation thereto, and an element of conducting material movable with respect to the sleeve in unison with said core to provide a variable capacity with said sleeve, a second tunable circuit including said variable capacity and means providing an adjustable connection between said coreand said movable element to adjust the tracking relation in the tuning of said circuits.

4. A unitary tuning system comprising two circuits, a variable capacitor device in one circuit and a variable inductance device in the other circuit, each of said variable devices having a movable and a fixed element, said elements being coaxially arranged and said movable elements being coextensively movable, and means for adjusting the relation between the movable elements of said capacitor and inductance devices, whereby simultaneous variation of capacity and inductance for predetermined tracking relation in the tuning of said circuits is provided.

5. In a superheterodyne receiving system, a radio frequency and oscillator tuning unit comprising a variable permeability oscillator tuning winding, a high frequency input circuit, and a variable capacitor for tuning said circuit comprising tubular conducting elements connected with said circuit and surrounding said inductance in spaced relation to each other to provide an electromagnetic shield therefor.

WILLIAM F. SANDS. GEORGE M. DALY. 

